feat: add hard mode and weekly mutation system

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

game/mutation.go

@@ -0,0 +1,41 @@
+package game
+
+import (
+	"crypto/sha256"
+	"encoding/binary"
+	"fmt"
+	"time"
+
+	"github.com/tolelom/catacombs/config"
+)
+
+// Mutation represents a weekly gameplay modifier.
+type Mutation struct {
+	ID          string
+	Name        string
+	Description string
+	Apply       func(cfg *config.GameConfig)
+}
+
+// Mutations is the list of all available mutations.
+var Mutations = []Mutation{
+	{ID: "no_skills", Name: "Skill Lockout", Description: "Class skills are disabled",
+		Apply: func(cfg *config.GameConfig) { cfg.SkillUses = 0 }},
+	{ID: "speed_run", Name: "Speed Run", Description: "Turn timeout halved",
+		Apply: func(cfg *config.GameConfig) { cfg.TurnTimeoutSec = max(cfg.TurnTimeoutSec/2, 2) }},
+	{ID: "no_shop", Name: "Shop Closed", Description: "Shops are unavailable",
+		Apply: func(cfg *config.GameConfig) {}},
+	{ID: "glass_cannon", Name: "Glass Cannon", Description: "Double damage, half HP",
+		Apply: func(cfg *config.GameConfig) {}},
+	{ID: "elite_flood", Name: "Elite Flood", Description: "All monsters are elite",
+		Apply: func(cfg *config.GameConfig) {}},
+}
+
+// GetWeeklyMutation returns the mutation for the current week,
+// determined by a SHA-256 hash of the year and ISO week number.
+func GetWeeklyMutation() Mutation {
+	year, week := time.Now().ISOWeek()
+	h := sha256.Sum256([]byte(fmt.Sprintf("mutation:%d:%d", year, week)))
+	idx := int(binary.BigEndian.Uint64(h[:8]) % uint64(len(Mutations)))
+	return Mutations[idx]
+}

game/mutation_test.go

@@ -0,0 +1,68 @@
+package game
+
+import (
+	"testing"
+
+	"github.com/tolelom/catacombs/config"
+)
+
+func TestGetWeeklyMutation(t *testing.T) {
+	m := GetWeeklyMutation()
+	if m.ID == "" {
+		t.Error("expected non-empty mutation ID")
+	}
+	if m.Name == "" {
+		t.Error("expected non-empty mutation Name")
+	}
+	if m.Apply == nil {
+		t.Error("expected non-nil Apply function")
+	}
+	// Verify it returns one of the known mutations
+	found := false
+	for _, known := range Mutations {
+		if known.ID == m.ID {
+			found = true
+			break
+		}
+	}
+	if !found {
+		t.Errorf("mutation ID %q not found in Mutations list", m.ID)
+	}
+}
+
+func TestMutationApplyNoSkills(t *testing.T) {
+	cfg := config.GameConfig{SkillUses: 3}
+	// Find the no_skills mutation
+	var m Mutation
+	for _, mut := range Mutations {
+		if mut.ID == "no_skills" {
+			m = mut
+			break
+		}
+	}
+	if m.ID == "" {
+		t.Fatal("no_skills mutation not found")
+	}
+	m.Apply(&cfg)
+	if cfg.SkillUses != 0 {
+		t.Errorf("expected SkillUses=0 after no_skills mutation, got %d", cfg.SkillUses)
+	}
+}
+
+func TestMutationApplySpeedRun(t *testing.T) {
+	cfg := config.GameConfig{TurnTimeoutSec: 10}
+	var m Mutation
+	for _, mut := range Mutations {
+		if mut.ID == "speed_run" {
+			m = mut
+			break
+		}
+	}
+	if m.ID == "" {
+		t.Fatal("speed_run mutation not found")
+	}
+	m.Apply(&cfg)
+	if cfg.TurnTimeoutSec != 5 {
+		t.Errorf("expected TurnTimeoutSec=5 after speed_run mutation, got %d", cfg.TurnTimeoutSec)
+	}
+}

game/session.go

@@ -73,15 +73,17 @@ func (s *GameSession) clearLog() {
 }
 
 type GameSession struct {
-	mu           sync.Mutex
-	cfg          *config.Config
-	state        GameState
-	started      bool
-	actions      map[string]PlayerAction // playerName -> action
-	actionCh     chan playerActionMsg
-	combatSignal chan struct{}
-	done         chan struct{}
-	lastActivity map[string]time.Time // fingerprint -> last activity time
+	mu             sync.Mutex
+	cfg            *config.Config
+	state          GameState
+	started        bool
+	actions        map[string]PlayerAction // playerName -> action
+	actionCh       chan playerActionMsg
+	combatSignal   chan struct{}
+	done           chan struct{}
+	lastActivity   map[string]time.Time // fingerprint -> last activity time
+	HardMode       bool
+	ActiveMutation *Mutation
 }
 
 type playerActionMsg struct {